Wavelength conversion member and production method therefor

ABSTRACT

Provided is a wavelength conversion member that can be readily adjusted in chromaticity and can be increased in productivity and a production method for the wavelength conversion member. A wavelength conversion member 1 having a first principal surface 1a and a second principal surface 1b opposed to each other includes a glass matrix 2 and phosphor particles 3 disposed in the glass matrix 2, wherein concentrations of the phosphor particles 3 in the first principal surface 1a and in the second principal surface 1b are higher than concentrations of the phosphor particles 3 in surface layer bottom planes 1c and 1d located 20 μm inward from the first principal surface 1a and 20 μm inward from the second principal surface 1b, respectively.

TECHNICAL FIELD

The present invention relates to wavelength conversion members forconverting the wavelength of light emitted from a light emitting diode(LED), a laser diode (LD) or the like to another wavelength andproduction methods therefor.

BACKGROUND ART

Recently, attention has been increasingly focused on light emittingdevices and the like using LEDs or LDs, as next-generation light sourcesto replace fluorescence lamps and incandescent lamps. As an example ofsuch a next-generation light source, there is a disclosure of a lightemitting device in which an LED for emitting a blue light is combinedwith a wavelength conversion member capable of absorbing part of thelight from the LED to convert it to a yellow light. This light emittingdevice emits a white light which is a synthesized light of the bluelight emitted from the LED and the yellow light emitted from thewavelength conversion member. Patent Literature 1 proposes, as anexample of a wavelength conversion member, a wavelength conversionmember in which phosphor powder is dispersed in a glass matrix.

CITATION LIST Patent Literature

-   [PTL 1]-   JP-A-2003-258308

SUMMARY OF INVENTION Technical Problem

Such a wavelength conversion member as described in Patent Literature 1is made by polishing a glass-based material including phosphor powderdispersed in a glass matrix to reduce its thickness. However, the amountof glass-based material ground away for obtaining a wavelengthconversion member having a desired chromaticity may become large, sothat productivity cannot sufficiently be increased.

An object of the present invention is to provide a wavelength conversionmember that can be readily adjusted in chromaticity and can be increasedin productivity and a production method for the wavelength conversionmember.

Solution to Problem

A wavelength conversion member according to the present invention is awavelength conversion member having a first principal surface and asecond principal surface opposed to each other and includes a glassmatrix and phosphor particles disposed in the glass matrix, whereinconcentrations of the phosphor particles in the first principal surfaceand in the second principal surface are higher than concentrations ofthe phosphor particles in portions 20 μm inward from the first principalsurface and 20 μm inward from the second principal surface.

It is preferred that a concentration of the phosphor particles in amiddle portion between the first principal surface and the secondprincipal surface be low and a concentration of the phosphor particlesincrease toward the first principal surface and toward the secondprincipal surface.

A method for producing a wavelength conversion member according to thepresent invention is a method for producing the wavelength conversionmember constructed according to the present invention and includes thesteps of: preparing a slurry containing glass particles to be the glassmatrix and the phosphor particles; applying the slurry to substrates,drying the slurry, and allowing the phosphor particles to sedimentdownward before completion of the drying to obtain first and secondgreen sheets in each of which a concentration of the phosphor particlesin an under surface is higher than a concentration of the phosphorparticles in a top surface; and stacking the first and second greensheets so as to superpose the top surfaces thereof and bonding andfiring the first and second green sheets together.

The method preferably further includes the step of polishing the firstprincipal surface and/or the second principal surface of the wavelengthconversion member.

Advantageous Effects of Invention

The present invention enables provision of a wavelength conversionmember capable of being readily adjusted in chromaticity and capable ofbeing increased in productivity and a production method for thewavelength conversion member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional front view of a wavelengthconversion member according to a first embodiment of the presentinvention.

FIG. 2 is a schematic plan view showing the concentration of phosphorparticles in a first principal surface of the wavelength conversionmember according to the first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional plan view showing theconcentration of phosphor particles in a surface layer bottom plane 20μm inward from the first principal surface of the wavelength conversionmember according to the first embodiment of the present invention.

FIGS. 4(a) to 4(d) are schematic cross-sectional front views forillustrating an example of a method for producing the wavelengthconversion member according to the first embodiment of the presentinvention.

FIG. 5 is a schematic cross-sectional front view of a wavelengthconversion member according to a second embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a description will be given of preferred embodiments.However, the following embodiments are merely illustrative and thepresent invention is not limited to the following embodiments.Throughout the drawings, members having substantially the same functionsmay be referred to by the same reference characters.

First Embodiment

FIG. 1 is a schematic cross-sectional front view of a wavelengthconversion member according to a first embodiment of the presentinvention. As shown in FIG. 1, a wavelength conversion member 1 includesa glass matrix 2 and phosphor particles 3 disposed in the glass matrix2. The wavelength conversion member 1 has first and second principalsurfaces 1 a, 1 b opposed to each other.

In this embodiment, the first principal surface 1 a is an incidentsurface allowing excitation light to be incident thereon. The phosphorparticles 3 emit fluorescence upon entry of excitation light into thewavelength conversion member 1. The second principal surface 1 b is anexit surface allowing the fluorescence and the excitation light to exitthe wavelength conversion member 1 therethrough. Note that in thisembodiment the direction in which the first principal surface 1 a andthe second principal surface 1 b are opposed to each other is athickness direction.

No particular limitation is placed on the type of the glass matrix 2 solong as it can be used as a dispersion medium for the phosphor particles3, such as inorganic phosphor. For example, borosilicate glass,phosphate glass, tin-phosphate glass or bismuthate glass can be used.Examples of the borosilicate glass include those containing, in % bymass, 30 to 85% SiO₂, 0 to 30% Al₂O₃, 0 to 50% B₂O₃, 0 to 10%Li₂O+Na₂O+K₂O, and 0 to 50% MgO+CaO+SrO+BaO. Examples of thetin-phosphate glass include those containing, in % by mole, 30 to 90%SnO and 1 to 70% P₂O₅. The softening point of the glass matrix 2 ispreferably 250° C. to 1000° C., more preferably 300° C. to 950° C., andstill more preferably in a range of 500° C. to 900° C. If the softeningpoint of the glass matrix 2 is too low, the mechanical strength andchemical durability of the wavelength conversion member 1 may decrease.Furthermore, because the thermal resistance of the glass matrix 2 itselfdecreases, the wavelength conversion member 1 may be softened anddeformed by heat generated by the phosphor particles 3. On the otherhand, if the softening point of the glass matrix 2 is too high, thephosphor particles 3 may be deteriorated by a firing process duringproduction, so that the luminescence intensity of the wavelengthconversion member 1 may decrease. The glass matrix 2 is preferablyalkali-free glass. Thus, deactivation of the phosphor particles 3 can beprevented. From the viewpoint of increasing the mechanical strength andchemical durability of the wavelength conversion member 1, the softeningpoint of the glass matrix 2 is preferably not less than 500° C., morepreferably not less than 600° C., still more preferably not less than700° C., yet still more preferably not less than 800° C., andparticularly preferably not less than 850° C. An example of such a glassis borosilicate glass. However, if the softening point of the glassmatrix 2 rises, the firing temperature also rises and, as a result, theproduction cost tends to rise. Therefore, from the viewpoint ofinexpensively producing the wavelength conversion member 1, thesoftening point of the glass matrix 2 is preferably not more than 550°C., more preferably not more than 530° C., still more preferably notmore than 500° C., yet still more preferably not more than 480° C., andparticularly preferably not more than 460° C. Examples of such a glassinclude tin-phosphate glass and bismuthate glass.

No particular limitation is placed on the type of the phosphor particles3 so long as they emit fluorescence upon entry of excitation light. Aspecific example of the type of the phosphor particles 3 is one or moreselected from the group consisting of oxide phosphor, nitride phosphor,oxynitride phosphor, chloride phosphor, oxychloride phosphor, sulfidephosphor, oxysulfide phosphor, halide phosphor, chalcogenide phosphor,aluminate phosphor, halophosphoric acid chloride phosphor, andgarnet-based compound phosphor. When using a blue light as theexcitation light, for example, a phosphor emitting a green light, ayellow light or a red light as fluorescence can be used.

The average particle diameter of the phosphor particles 3 is preferably1 μm to 50 μm and more preferably 5 μm to 25 μm. If the average particlediameter of the phosphor particles 3 is too small, the luminescenceintensity may decrease. On the other hand, if the average particlediameter of the phosphor particles 3 is too large, the luminescent colormay be uneven.

The content of the phosphor particles 3 in the glass matrix 2 ispreferably in a range of 1 to 70% by volume, more preferably in a rangeof 1.5 to 50% by volume, and still more preferably in a range of 2 to30% by volume. If the content of the phosphor particles 3 is too small,the luminescence intensity of the wavelength conversion member 1 may beinsufficient. On the other hand, if the content of the phosphorparticles 3 is too large, a desired luminescent color may not be able tobe obtained. In addition, the mechanical strength of the wavelengthconversion member 1 may decrease.

The thickness of the wavelength conversion member 1 is preferably in arange of 0.01 mm to 1 mm, more preferably in a range of 0.03 mm to 0.5mm, still more preferably in a range of 0.05 mm to 0.35 mm, particularlypreferably in a range of 0.075 mm to 0.3 mm, and most preferably in arange of 0.1 mm to 0.25 mm. If the thickness of the wavelengthconversion member 1 is too large, scattering and absorption of light inthe wavelength conversion member 1 may become too much, so that theefficiency of emission of fluorescence may become low. If the thicknessof the wavelength conversion member 1 is too small, sufficientluminescence intensity may be less likely to be obtained. In addition,the mechanical strength of the wavelength conversion member 1 may beinsufficient.

A feature of this embodiment is that the concentrations of phosphorparticles 3 in the first principal surface 1 a and in the secondprincipal surface 1 b are higher than the concentrations of phosphorparticles 3 in portions 20 μm inward from the first principal surface 1a and 20 μm inward from the second principal surface 1 b. A descriptionwill be given of the feature of this embodiment with reference to FIGS.1 to 3.

As shown in FIG. 1, in this embodiment, a plane of the wavelengthconversion member 1 located 20 μm inward from the first principalsurface 1 a is referred to as a surface layer bottom plane 1 c.Likewise, a plane of the wavelength conversion member 1 located 20 μminward from the second principal surface 1 b is referred to as a surfacelayer bottom plane 1 d. A region from the first principal surface 1 a tothe surface layer bottom plane 1 c and a region from the secondprincipal surface 1 b to the surface layer bottom plane 1 d are surfacelayers B in this embodiment. Furthermore, a region between the surfacelayer bottom plane 1 c and the surface layer bottom plane 1 d is amiddle portion A in this embodiment.

FIG. 2 is a schematic plan view showing the concentration of phosphorparticles 3 in the first principal surface 1 a. FIG. 3 is a schematiccross-sectional plan view showing the concentration of phosphorparticles 3 in the surface layer bottom plane 1 c located 20 μm inwardfrom the first principal surface 1 a. As shown in FIGS. 2 and 3, thearea occupancy of phosphor particles 3 in the first principal surface 1a is larger than that of phosphor particles 3 in the surface layerbottom plane 1 c. Therefore, the concentration of phosphor particles 3in the first principal surface 1 a is higher than that of phosphorparticles 3 in the surface layer bottom plane 1 c located 20 μm inwardfrom the first principal surface 1 a.

Likewise, on the second principal surface 1 b side, the area occupancyof phosphor particles 3 in the second principal surface 1 b is largerthan that of phosphor particles 3 in the surface layer bottom plane 1 d.Therefore, the concentration of phosphor particles 3 in the secondprincipal surface 1 b is higher than that of phosphor particles 3 in thesurface layer bottom plane 1 d located 20 μm inward from the secondprincipal surface 1 b.

The area occupancy of phosphor particles 3 in each of the firstprincipal surface 1 a and the second principal surface 1 b is preferablynot less than 140% of the area occupancy of phosphor particles 3 in eachof the surface layer bottom plane 1 c and the surface layer bottom plane1 d, more preferably not less than 160% thereof, still more preferablynot less than 200% thereof, preferably not more than 1000% thereof, morepreferably not more than 500% thereof, and still more preferably notmore than 330% thereof. If the area occupancy is too small, the amountof change in chromaticity upon polishing is too small, so that theproduction efficiency tends to decrease. On the other hand, if the areaoccupancy is too large, the amount of change in chromaticity uponpolishing is too large, which makes it difficult to adjust thechromaticity with high accuracy.

The area occupancy is calculated by digitizing each of SEM (scanningelectron microscopic) images of the principal surfaces and surface layerbottom planes and determining the proportion of the area of portionsoccupied by phosphor particles per unit area of the image. As for thesurface layer bottom planes, their images are taken with the surfacelayer bottom planes exposed by polishing the principal surfaces.

In this embodiment, the concentration of phosphor particles 3 in themiddle portion A between the first principal surface 1 a and the secondprincipal surface 1 b is low and the concentration of phosphor particles3 increases toward the first principal surface 1 a and toward the secondprincipal surface 1 b. More specifically, the wavelength conversionmember 1 according to this embodiment has a concentration gradient inwhich the concentration of phosphor particles 3 gradually increases fromthe center of the middle portion A toward the first principal surface 1a and toward the second principal surface 1 b. Therefore, the surfacelayers B also have a concentration gradient in which the concentrationof phosphor particles 3 gradually increases toward the first principalsurface 1 a and toward the second principal surface 1 b. Although inFIG. 1 the phosphor particles 3 are not shown in the middle portion A,the middle portion A may also contain the phosphor particles 3 as shownin FIG. 3. For the purpose of showing a high concentration of phosphorparticles 3 in the surface layers B, FIG. 1 shows the phosphor particles3 in the surface layers B only.

The wavelength conversion member 1 is used for the purpose of convertingthe wavelength of entered excitation light and emitting fluorescence. Inthe case of a white light emitting device, a white light, for example,which is a synthesized light of a blue light as excitation light from alight source, such as an LED, and a yellow light as fluorescence, isemitted from the wavelength conversion member 1. The adjustment of thechromaticity of light to be emitted from the wavelength conversionmember 1 is generally achieved by polishing at least one of the firstprincipal surface 1 a and the second principal surface 1 b of thewavelength conversion member 1 to reduce the thickness of the wavelengthconversion member 1. By reducing the thickness of the wavelengthconversion member 1, the proportion of fluorescence emitted from thewavelength conversion member 1 can be reduced and the proportion ofexcitation light passing through the wavelength conversion member 1 canbe increased. The adjustment of the thickness of the wavelengthconversion member 1 is generally achieved by polishing within theregions of the surface layers B.

In this embodiment, the concentrations of phosphor particles 3 in thefirst principal surface 1 a and in the second principal surface 1 b arehigher than the concentrations of phosphor particles 3 in the surfacelayer bottom plane 1 c and in the surface layer bottom plane 1 d.Therefore, the change in chromaticity relative to the change inthickness due to polishing of the first principal surface 1 a or thesecond principal surface 1 b is large. In other words, the chromaticitycan be largely changed even if the amount of material ground away bypolishing is small and, therefore, the chromaticity can be readilyadjusted. Hence, according to this embodiment, the chromaticity can bereadily adjusted, so that the productivity can be increased.

Hereinafter, a description will be given of an example of a method forproducing the wavelength conversion member 1.

(Method for Producing Wavelength Conversion Member)

FIGS. 4(a) to 4(d) are schematic cross-sectional front views forillustrating an example of a method for producing the wavelengthconversion member according to the first embodiment.

In the method for producing the wavelength conversion member 1, first, aslurry is prepared which contains glass particles to be a glass matrix,phosphor particles, and organic components including a binder resin anda solvent. Next, as shown in FIG. 4(a), the slurry 4 is applied onto aresin film 6 made of polyethylene terephthalate or other resins andserving as a substrate, by the doctor blade method or other methods.

Next, the slurry 4 is dried. In doing so, the phosphor particles 3 areallowed to sediment downward before the completion of the drying of theslurry 4. Thus, as shown in FIG. 4(b), a first green sheet 5A isobtained in which the concentration of phosphor particles 3 in the undersurface 5Ab is higher than the concentration of phosphor particles 3 inthe top surface 5Aa.

Note that the density of glass particles in the slurry 4 is smaller thanthe density of phosphor particles 3 therein. Therefore, the phosphorparticles 3 can be suitably allowed to sediment. Thus, in the firstgreen sheet 5A, the above-mentioned concentration distribution of thephosphor particles 3 can be more securely achieved.

On the other hand, a second green sheet 5B shown in FIG. 4(c) isobtained in the same manner as the process shown in FIGS. 4(a) and 4(b).Also in the second green sheet 5B, the concentration of phosphorparticles 3 in the under surface 5Bb is higher than the concentration ofphosphor particles 3 in the top surface 5Ba.

Next, as shown in FIG. 4(c), the first and second green sheets 5A, 5Bare stacked so as to superpose their top surfaces 5Aa, 5Ba. Next, thefirst and second green sheets 5A, 5B are bonded together by theapplication of heat and pressure and fired. Thus, a wavelengthconversion member 1A shown in FIG. 4(d) is produced.

In addition, both or one of the first principal surface 1 a and thesecond principal surface 1 b of the wavelength conversion member 1A maybe polished to adjust the chromaticity of the wavelength conversionmember 1A. In the first embodiment, the first and second principalsurfaces 1 a, 1 b are polished, thus obtaining the wavelength conversionmember 1 shown in FIG. 1. No particular limitation is placed on thepolishing method and it can be provided, for example, by lapping ormirror polishing. Lapping has the advantage of having a higher polishingspeed than mirror polishing. On the other hand, mirror polishing canincrease the accuracy of a polished surface as compared to lapping. Thethickness and chromaticity of the wavelength conversion member 1A have acorrelation. Therefore, if this correlation is previously determined, atarget thickness of the wavelength conversion member 1A for obtaining adesired chromaticity can be determined. The correlation between thethickness and the chromaticity can be determined, for example, bymeasuring the thickness and chromaticity while keeping on polishing inconditions of higher chromaticity than a target chromaticity. In thiscase, from the viewpoint of determining the correlation betweenchromaticity and thickness with high accuracy, it is preferred to adopta polishing method providing a surface condition (surface roughness)equivalent to that of the finished surface of a final product. Forexample, if the product is finished by mirror polishing, mirrorpolishing is preferably also adopted in the polishing method fordetermining the correlation between chromaticity and thickness.

Second Embodiment

FIG. 5 is a schematic cross-sectional front view of a wavelengthconversion member according to a second embodiment. A wavelengthconversion member 11 according to this embodiment can be produced bystacking not only the first and second green sheets 5A, 5B shown in FIG.4(c) but also a third green sheet made in the same manner as for thefirst and second green sheets 5A, 5B. Specifically, the wavelengthconversion member 11 can be produced by laying the top surface of thethird green sheet, the top surface having a lower concentration ofphosphor particles 3, on the laminate of the first and second greensheets 5A, 5B and bonding and firing them together.

Also in this embodiment, the concentrations of phosphor particles 3 in afirst principal surface 11 a and in a second principal surface 11 b arehigher than the concentrations of phosphor particles 3 in a surfacelayer bottom plane 11 c and in a surface layer bottom plane 11 d.Therefore, even if the amount of material ground away by polishing thefirst principal surface 11 a or the second principal surface 11 b issmall, the chromaticity can be largely changed. Hence, the chromaticitycan be readily adjusted, so that the productivity can be increased.

REFERENCE SIGNS LIST

-   -   1, 1A . . . wavelength conversion member    -   1 a, 1 b . . . first and second principal surfaces    -   1 c, 1 d . . . surface layer bottom plane    -   2 . . . glass matrix    -   3 . . . phosphor particle    -   4 . . . slurry    -   5A . . . first green sheet    -   5Aa . . . top surface    -   5Ab . . . under surface    -   5B . . . second green sheet    -   5Ba . . . top surface    -   5Bb . . . under surface    -   6 . . . resin film    -   11 . . . wavelength conversion member    -   11 a, 11 b . . . first and second principal surfaces    -   11 c, 11 d . . . surface layer bottom plane    -   A . . . middle portion    -   B . . . surface layer

1. A wavelength conversion member having a first principal surface and asecond principal surface opposed to each other, the wavelengthconversion member comprising: a glass matrix; and phosphor particlesdisposed in the glass matrix, wherein concentrations of the phosphorparticles in the first principal surface and in the second principalsurface are higher than concentrations of the phosphor particles inportions 20 μm inward from the first principal surface and 20 μm inwardfrom the second principal surface.
 2. The wavelength conversion memberaccording to claim 1, wherein a concentration of the phosphor particlesin a middle portion between the first principal surface and the secondprincipal surface is low and a concentration of the phosphor particlesincreases toward the first principal surface and toward the secondprincipal surface.
 3. A method for producing the wavelength conversionmember according to claim 1, the method comprising the steps of:preparing a slurry containing glass particles to be the glass matrix andthe phosphor particles; applying the slurry to substrates, drying theslurry, and allowing the phosphor particles to sediment downward beforecompletion of the drying to obtain first and second green sheets in eachof which a concentration of the phosphor particles in an under surfaceis higher than a concentration of the phosphor particles in a topsurface; and stacking the first and second green sheets so as tosuperpose the top surfaces thereof and bonding and firing the first andsecond green sheets together.
 4. The method for producing the wavelengthconversion member according to claim 3, further comprising the step ofpolishing the first principal surface and/or the second principalsurface of the wavelength conversion member.